Affordable Small Block Race Engine - Cheap Street Secrets

Cheap Street rules dictate a 385-cid maximum displacement, although there's a 10-pound penalty for every cube over 365. And with this engine destined for a Third-Gen Camaro, which already carries a weight penalty compared to pre-'75 cars in the class, the owner didn't want to add even more weight with a bigger-inch engine. So, this 350 block received just the standard .030-in. overbore, for a grand total of 355 ci.

The rules are pretty simple: build a low-dough motor with an iron block, off-the-shelf heads, an off-the-shelf carb, and a shot of juice. Don't go overboard on the trick parts, though, because the guy next to you can buy your engine for $3,000.

Welcome to Cheap Street competition. PRO bills it as the ultimate "real world" class in its pro series, with the competitors driving street-based combinations-more or less. And to keep the competition relatively attainable to checkbook-challenged racers, the class has adopted a longstanding tradition in the sportsman circle track world: claimer engines.

In Cheap Street, a racer who believes another competitor might have an unfair edge can claim that competitor's long block for $3,000, as well as a transmission for $2,000 and even the carburetor for $500. It keeps the players on a level playing field on oval tracks, and, theoretically, ought to do the same in this heads-up, wheels-up class.

But drag racers are a notoriously crafty bunch, and being competitive in Cheap Street requires at least 600 horses and high-9-second e.t.'s. That's a lot to ask of car weighing a minimum of 3,200 pounds and powered by a stock-headed small-block.

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Fortunately, the engine was a four-bolt-main 350. Because main bolts stretch when installed and removed, which is likely to happen during the course of the racing season, a few bucks was spent to install studs for securing the main caps. This also makes removal and re-installation a little quicker.

We recently followed the build of a Cheap Street engine at Thomson Automotive, a Detroit-area shop run by longtime racer Brian Thomson. He's been building drag race and circle track engines for more than 20 years and he said he was confident he could find the maximum power with the parts allowed.

But what are the parts allowed? Good question. Here's an overview of the Cheap Street rulebook:*Iron small-block displacing no more than 385 ci*Mass-produced cast iron or aluminum heads; millingpermitted, but no porting, welding or epoxy allowed*Maximum valve sizes of 2.025 intake, 1.610 exhaust*Flat top pistons only*No roller cam allowed*Nitrous oxide allowed, but only with single stage system, maximum jet size of 0.063 inch.*No more than a single 750-cfm carburetor; "typical" carb mods allowed*Exhaust pipes have a maximum 3-inch tubing diameter*Supercharging, turbocharging, and fuel injection prohibited

A relatively inexpensive method to ensure the racing engine's longevity, especially since it'll be on nitrous for each pass down the track, is filling the water jackets with cement, which prevents the cylinders from deforming. In this case, Thomson Automotive used Hard Blok jacket filler, which is a cement-based product designed for use in racing engines. Its coefficient of thermal expansion is the same as iron engine blocks. Thomson leaves enough room in the water jackets to allow water to get to the heads.

"It's harder than it looks," says Thomson. "The easy way to make power, even with stock-type heads, is to add compression. The flat-tops limit compression severely, and the tiny nitrous jet certainly won't double the engine's output."

And, there's the weight factor: Pre-'75 cars and all trucks in Cheap Street must weigh 3,200 pounds if equipped with at least a 365-cid engine; it's 3,250 for '75-and-later cars. However, a weight penalty of 10 pounds per cubic inch is assessed for each cube over 365.

The engine Thomson built for this story was headed for a Third-Gen F-car, meaning it would have to weigh at least 3,250 pounds.

"The owner wants to avoid adding weight, so we decided to keep the engine under 365 cubic inches," says Thomson.

Firm FoundationAlthough cognizant of the claimer rule, Thomson and the engine's owner knew there was no way to build a competitive engine for $3,000-and make it last for an entire racing season. The decision was made to use the strongest parts where possible, knowing that items like the unmodified heads, intake and carb would be relatively affordable.

Rather than start with an all-new short-block, however, Thomson started with a used block and cleaned it up. By giving it the standard 0.030-inch overbore and a 350 crank, the engine would displace 355 ci.

The rotating assembly was built for durability, low mass and low friction. The lightweight Diamond aluminum pistons and GRP aluminum rods from GRP aren't exactly cheap, but they provide a necessary performance edge, according to Thomson.

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Another used part in the Cheap Street engine is the forged steel crank. Reconditioned and balanced, the 10-10 crank also was nitrided and ought to provide sturdy, reliable service for a long time.

"We wanted to do anything within the rules to lighten the rotating mass of the assembly," he says. "The Diamond pistons have a Teflon coating to reduce friction; it all contributes to speeding up the rotating assembly."

Another trick employed was sealing off the oil return passages at the top of the block, which keeps oil at the bottom of the engine. Within the block, of course, turns the camshaft. We tried with flattery, beer, and money, but couldn't pry its specs from the engine builder.

"It's a Thomson special grind," he says with a grin. "It's the key to this engine's power."

In fact, all we could get out of the tight-lipped Thomson was, "it's a flat-tappet cam."

He also was mum about the compression ratio. The engine uses Vortec iron cylinder heads (GM PN 12558060), which aren't particularly known for their high-rpm flow characteristics, but do have relatively efficient combustion chambers.

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The rules say a wet sump oiling system must be used, so a deep-sump, yet lightweight, aluminum pan was created for the small-block. It was designed to hold extra oil while fitting the contours of the Third-Gen Camaro's chassis.

Because head milling is permitted, Thomson touched the bottoms of the Vortecs, but doesn't want to reveal how much because doing so, he says, would reveal the approximate combustion chamber volume and, thus, the compression.

"There's no technical limit on compression in the rules, but the flat-top pistons effectively limit it," he says. "It's a delicate balance between higher compression and valve interference; the cam also has something to do with it. Next question, please."

Uh, not so fast. According to our copy of the GM Performance Parts catalog, the maximum lift for a camshaft used with the Vortec heads is .475-inch. Those of you who are good with a slide rule can now make some calculations regarding the cam's specs and the engine's compression ratio.

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Nothing exotic here: just an inexpensive double-row timing chain setup from the GM Performance Parts catalog. The double row design adds durability to the engine without breaking the budget.

We'll give you a hint to get started: Most engines in this class will have compression ratios from around 10:1 to 12:1.

Minimal SqueezeAlthough mum about the cam and compression, Thomson was chatty when it came to the engine's induction and fuel delivery, which is a simple, single-plain high-rpm manifold topped with one of Barry Grant's Demon 750 carburetor-a Mighty Demon, to be precise.

"Works terrific for high-rpm power," says Thomson. "With the heads being somewhat restrictive in their flow, it was important to get as much air through them as they could take. The Demon is also pretty easy to adjust in the pits."

Indeed, it was designed for between-rounds tweaks, according to Barry Grant Inc.'s Steve Cole.

"It's the perfect kind of carburetor for Cheap Street because it was designed for the types of adjustments racers make at the track," he says.

And with a $500 claim for the carb in Cheap Street, the carb can be purchased for just about that price.

"The Mighty Demon really is hybrid of the street-based Speed Demon carb and the Race Demon," he says. "Actually, once the jet extensions are added and the floats swapped, the Mighty Demon has the features of the Race Demon. For this type of competition, it's really the logical choice."

Between the carb and intake sits a half-inch plate for a Nitrous Works laughing gas system, fitted with the rules-specific 0.063-inch jet. The rules also state the system can only have one fuel spray bar and one nitrous spray bar.

"It's pretty small and the rules are very specific about it," says Thomson of the nitrous jet. "To make it [the nitrous system] the most effective, you have to really get the bottle pressure up. Way up."

All of Thomson's tricks, including those he would and would not tell us, seem to have paid off. On the dyno, the engine produced 479 hp and 447 ft-lb of torque without nitrous.

The broad power curves of the 4,000-6,800-rpm band, where the engine will operate most of the time, show more than 400 ft-lb of torque by 4,400 rpm and holding above that mark until at least 6,300 rpm. In fact, the engine makes 380 ft-lb at 6,600 rpm.

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Another stipulation of the rules is flat-top pistons. Combined with the limited number of legal cylinder heads, compression ratio of the class's engines typically falls in the 10:1 to 12:1 range. Thomson makes the most of the rules, however, by using lightweight Diamond aluminum pistons that have a friction-reducing Teflon coating on the sides. Combined with lightweight GRP rods Thomson keeps the weight of the reciprocating assembly as low as possible, which allows the engine to rev higher and faster.

As for horsepower, the engine makes 450 by about 5,400 rpm and holds between that mark and the 479 peak until 6,800 rpm. On the dyno the nitrous kicked in at about 5,200 rpm and simply added 120-150 horses throughout the rest of the rpm range.

Thomson is certainly happy with the engine's performance, but the rules of Cheap Street are things by which he's not used to being limited.

"For a combination with no real compression, I think it made really good power," he says. "We were limited by the rules, but we also used the letter of them to any advantage we could take."

There, of course, lies the unknown. Other builders undoubtedly have bent the rules without breaking them-it's the nature of racing. And until the engine's owner is able to get his car to the track, it'll be difficult to judge whether Thomson built a big enough stick for the fight.

"At the very least, our engine should be reliable and get through the season with minimal tear-downs," he says. "It should also be quite competitive. The power is good."

Like we said, Thomson wouldn't reveal every secret to his Cheap Street recipe-and if you think any of the other competitors built a durable, competitive nitrous motor for just $3,000, give us a call; we've got a rust-free Mopar we want to sell you.

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Here's the camshaft. "It's a flat tappet cam," is all Brian Thomson will say about its specs. We do know that the iron GM Vortec heads used on the engine warn against using a cam with lift greater than .475-inch. Duration, centerline, and overlap are secrets Thomson won't reveal. "It's the key to the engine's power," he says.

Still, no matter how you look at it, 649 horses is darn good for a 355 with a used block and crank.

In other words, Cheap Street sounds a lot like Fun Street to us.

Off The Sidelines:GM Performance Parts' Gary Penn dives into Cheap StreetTalk a few minutes with Gary Penn and you'll know right away he's a racing enthusiast.

In fact, if you've been to an IHRA race, PRO race or even a Super Chevy Show during the last few years, there's a good chance you have spoken with Penn. During race weekends, he's usually found under the yellow awning of the GM Performance Parts trailer, dispensing catalogs, stickers and wisdom from his almost "Rainman"-like knowledge of Chevy engines.

But after several years of watching the races, Penn has decided to get involved. He's built a Camaro to compete in the six-race PRO Cheap Street series.

"I've been racing since I was 16," says the 41-year-old Penn. "It's in the blood."

Penn found a tired '86 Camaro and sent it to Tom Lukans, at TL Race Cars in Jonesville, South Carolina, where it is currently undergoing a transformation from street beater to track heater. Although the Cheap Street series advocates restraint through its $3,000 claimer engine clause, that hasn't stopped Penn and Lukans from building a professional car.

Per the rules, Penn will run a small-block conforming to a 385-cid maximum displacement and single stage of nitrous. It'll be backed by a Hughes Performance Turbo 350 with a full manual valve body and trans brake. The converter has a 5,000 stall speed, and the rearend is a Moser 12-bolt with a spool.

The combination should be good for 9.70-9.80 e.t.'s, according to Penn.

"I'm just looking to get back into racing and have some fun," he says. "There are only six Cheap Street races and prize money is negligible; I just want to stay in the game."

Whether he's in the staging lane or under the big yellow awning, Gary Penn isn't far from the action.

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